The present invention relates to the correction of malocclusion of teeth and more particularly to an appliance and method which utilizes light, continuous forces, virtually absent any torque, to accomplish these corrections.
An almost limitless variety of misalignments of teeth, deviating from what is considered normal for a pleasing facial appearance and for eating food properly, is encountered in orthodontic practice. Using current methods and appliances it has been found possible to move teeth bodily in nearly all directions. For example, teeth may be moved mesially (towards the midline of the mouth) or distally (away from the midline of the mouth), occlusally (towards the biting surfaces), gingivally (towards the gums), lingually (towards the tongue), or buccally (towards the cheek). A number of orthodontic appliances and methods are described in "Begg Orthodontic Theory and Technique"--Chapters 6 and 7 (1965--W. B. Saunders Company), the disclosure of which is hereby incorporated by reference.
In a typical procedure designed to correct malocclusions a wire usually referred to as an arch wire is placed across the dental arch of the upper teeth, and a second arch wire is placed across the dental arch of the lower teeth. Means are provided for securing the arch wire at each end of the dental arch. These arch wire securing means are usually metal bands placed around a posterior (most backwardly located in the mouth) tooth such as a first or second molar at both ends of both dental arches. The arch wires are further secured and guided across the dental arches by bracket means which are bonded to selected anterior (at or towards the front of the mouth) teeth such as the central and lateral incisors and the cuspids. A single bracket means is usually bonded directly onto the front surface of these teeth.
A major function of the arch wires is to provide a guide for the teeth so that they will move in a pre-selected direction during the course of treatment.
In this typical given example the arch wires have a second important function. The arch wires together with the securing brackets are designed to apply torque to the various teeth that are to be moved into a more correct alignment. To provide this torquing force the arch wires are rectangular, i.e. a cross section of the wire shows it to be rectangular in shape. The brackets cooperate with the arch wire in producing torque. Each bracket has a rectangular or square groove in order to engage the arch wire. This rectangular or square groove is not just a straight groove, but is placed in the bracket at an angle to the center plane of the bracket, usually a 5.degree. to 10.degree. angle. So now when these brackets are bonded to teeth, and the arch wire is to be placed within the grooves of these brackets, the arch wire must be twisted to gain entrance to the groove which is at a 5.degree. to 10.degree. angle in relation to the arch wire. The arch wire twisted in this manner will attempt to straighten itself out and in so doing torque will be applied to all of the bracketed teeth. Other tooth moving forces are also applied during treatment, such as the use of elastomeric bands attached at various positions to selected teeth. But it is to the use of torque producing rectangular arch wires and brackets with an angled rectangular or square groove that I wish to give particular attention.
In current orthodontic practice it is considered essential in most cases to apply this described torque in order to obtain optimum results. Although dramatic tooth movement can be obtained over a period of time using these appliances and techniques it has been my observation that a number of disadvantages often accompany such treatment. For example, root resorption may occur at the tips of the roots of front teeth, such as the central and lateral incisors, due to the prolonged application of torque. And bone destruction may occur at the gum line (gingival crest), which is known to promote periodontal breakdown. Also, joint problems at the junction of the upper and lower jaw (tempero-mandibular joint) are frequent sequela to these orthodentic procedures. Finally, the aesthetic appearance of the patient is often less than satisfactory since the excessive forces described tend to move the front teeth too far backward in the mouth, giving a pushed in facial appearance.
Accordingly it is an object to provide an appliance and method that will avoid root resorption.
Another object it to provide an appliance and method that will not cause destruction of bone at the gingival crest.
Another object is to provide an appliance and method that will avoid tempero-mandibular joint problems.
Another object is to provide an appliance and method that will improve facial aesthetics.
A further object is to provide an appliance and method to shorten treatment time to the 14 month level, with less patient discomfort and less patient cooperation required.